THE GROUND PLANE—FLOORS, STAIRS and RAMPS

The ground plane is the most fundamental element of interior design. It’s
the surface that supports all the activities, construction, and furnishings
that make up any interior space. As a basic enclosing surface, the ground plane,
like the overhead plane, represents a significant percentage of the total
surface area defining any room or space. It not only provides structural support and a
walking surface but also contributes significantly to the character and definition of the interior environment.

The ground plane must remain flat and level. Unlike walls, ceilings, furniture, and other
interior elements that can be angled, curved, and irregular, a floor must
essentially be a smooth surface, with only occasional interruptions with ramps
or stairs. The interior designer must express any design statement with material,
color, pattern, shape, or a change in level.

Floors support two types of elements, fixed and movable. Fixed elements
include construction such as partitions, cabinetry, and other raised floors.
Movable elements include furniture, equipment, and temporary constructions.
Fixed elements generally are perceived as part of the architecture of a space,
while movable elements read as furnishings.

The ground plane can be a neutral background for furniture and other elements
or it can be a major design statement in itself. The texture, color, and shapes
of the flooring material can also change the scale and character of the space
in which it’s used.

The interior designer can use the ground plane as a major design element,
while meeting all of the functional requirements of support, safety, durability, and accessibility.
This section discusses some of the design concepts that the designer can use
to begin thinking of the ground plane as a significant element and gives
some practical starting points for detailing.

Refer to Section 11 for more ideas on how to make transitions between ground
planes.

Because of the planar nature of floors and the strict needs for safety,
accessibility, and other functional requirements, there are fewer possible
structural concepts that the designer can use than might be possible with the
ceiling plane or with vertical barriers. However, even with these limitations,
the designer can develop a strong design statement by using flooring creatively and in
conjunction with the ceiling plane, vertical barriers, changes in level, and other
built-in construction.

Flooring

When sufficient space is not available for changes in level, the designer
can use the material, color, texture, and line of flooring materials as well
as changes of these elements within a single plane to express the design intent
of the space. --- shows some of these basic approaches.

Of course, the simplest approach is to use a single material as a background
for the activities, furniture, and other construction within the space. The
flooring material can be plain, textured, neutral, or boldly colored. The flooring
can have a strong directional line which can affect the dynamic, proportion, and scale
of a space.

However, as with ceiling patterns, a strong directional pattern should be
run perpendicular to the length of a space. Large patterns should generally
be used with large spaces and small patterns with smaller spaces. Small patterns
in a large space will sometimes be perceived as an overall tone rather than
individual visual texture.

Changes in material can be used to define space or for functional reasons.
E.g., hard surface flooring may be required next to carpet for durability in
a high-traffic area or for water resistance next to wet areas. The material
changes may be made with a simple line or more complex patterns.

Special patterns can also be designed as a design feature or to direct movement.
Flooring variations in a single plane are even more effective when coordinated
with changes in ceiling plane or material or used in conjunction with furniture
groupings. Although islands of different flooring can also be created with
area rugs, these may present a tripping hazard and may be difficult to maintain
in commercial uses.

The ground plane can be used most effectively to define space when a level
change is possible. Of course, this requires sufficient ceiling space, but
even a slight rise is sufficient to create a noticeable difference and create
the effect desired. In addition to the change in level itself, the line of
transition can be treated in various ways.

The designer can use stairs or ramps alone to make the transition or simply
have the change in level interrupted with railings or other features.

Stairs

Of course, when there is a change in level, the designer must provide a way
to move from one level to the other. This requires steps and usually an adjacent
ramp. Moving up and down just a few inches or a few feet within a space requires
a different design response than moving from one floor level to another. Although
there are some similar requirements of safety and comfort, floor-level changes
often require stairs that meet egress requirements, while minor level changes
are usually considered monumental stairs. This section only discusses small
changes in level requiring one to five steps as might be used for a small level
change.

One of the first decisions the designer must make is the height of the level
change and the number of steps. Although a platform with a single step up
is the easiest and least expensive to construct, single steps are inherently
dangerous and should usually be avoided. However, with careful design and inclusion
of handrails and visual clues identifying the level change, single-step level
changes may be used.

--- illustrates some of the ways short runs of steps can placed relative to
the level changes they serve. Straight, relatively narrow stairs are the most
efficient and safest. Wide stairs extending the full length of the level
change, create more of a design feature and allow movement over a wider area.
Wide stairs may require intermediate handrails for safety. Refer to the later
section in this section on constraints for a discussion of code requirements.
These types of stairs can be made safer by extending the depth of the tread
beyond the code minimum of 11 in. (279 mm).

Although stairs can be curved in plan or wrapped around an angle, these are
inherently more dangerous and should be used carefully with sufficient handrails and nosing
marking.. Other variations can be used. These provide a variation in the straight
run of stair but still provide for a walk path perpendicular to the width of
the stairway, which is safer than walking at an angle to each tread. Splayed
forms can be used to direct movement either at the top or bottom of the stair.

Ramps

Accessibility codes generally require ramps be provided for any change in
level. They may be used alone or in conjunction with steps. Because ramps require
significant amounts of floor area, the designer typically limits the height
of an optional platform created strictly for design reasons to minimize the
length of ramp required. However, in some situations the length along a ramp
may be used for other purposes. E.g., in a retail store, a display may be built
next to one side of a ramp, so the ramp serves for both circulation and merchandising.

--- illustrates some of the conceptual ways ramps can be placed relative to
level changes and in conjunction with steps. In most cases, especially in
public areas, both stairs and ramps should be provided. Some people with
mobility problems find it easier to use stairs than walk a longer distance
along a ramp. Ideally, the starting and ending points of both stairs and adjacent
ramps should be in the same area.

The designer should decide on how to place stairs and ramps based first
on the height the ramp must serve. A 21 in. (533 mm) level change will require
a much longer ramp than a 7 in. (178 mm) change, which may require a switchback
con figuration rather than a straight run.

More than any other design element, the ground plane requires the most attention
to its functional requirements. The floor of any space must provide a stable,
safe means of movement for people and a structurally sound platform for furniture and other
construction. Because of the amount of use the floor experiences, it must also
be durable for the type of use it’s put to and relatively easy to clean and otherwise
maintain. The ground plane should also provide the desired sense of movement and control
of circulation. Some of the other functional requirements include accessibility
for all users, comfort, water resistance, and sustainability.

Regardless of the approach the designer may take with the ground plane, these
functional requirements must be met. Refer to Sections
2 and 3 for further
discussion of basic constraints and functional requirements of details.

CONSTRAINTS

For the ground plane, constraints typically include the fire resistance of
the finish floor material and its support as well as the structural integrity and safety
of the floor. For changes in level, code requirements for safety and accessibility
must also be considered.

Fire Resistance of Floor Finishes

The IBC regulates the use of some finish flooring materials. These include
textile coverings or those composed of fibers, which is mainly carpet. The
IBC specifically excludes traditional flooring such as wood, vinyl, linoleum,
terrazzo, and other resilient floor coverings that are not composed of fibers.

The IBC requires textile or fiber floor coverings to be one of two classes
as defined by NFPA 253, the Flooring Radiant Panel Test. The NFPA 253 test
measures the flame spread in a corridor or exitway that is under the in fluence
of a fully developed fire in an adjacent space.

Class I materials are more resistant to flame spread than Class II materials.

In Groups I-1, I-2, and I-3 occupancies (such as assisted living facilities,
hospitals, nursing homes, and jails) the flooring finishes in exit enclosures
(stairways), exit passageways, and corridors must be Class I in a non-sprinklered
building and at least a Class II in a sprinklered building. Practically,
because the IBC also requires all I occupancies to be sprinklered, either Class
I or Class II is permissible. In other areas of Groups I-1, I-2, and I-3
occupancies, the flooring must be a Class II material.

For all other occupancy groups, the IBC requires that textile floor coverings
be a Class II material in nonsprinklered buildings. In sprinklered buildings,
textile flooring must meet the requirements of 16 CFR Part 1630, Standard for
the Surface Flammability of Carpets and Rugs.

This is also known as the methenamine pill test or simply the pill test. It’s
also referred to by other designations, DOC FF-1, Standard Test Method for
Flammability of Finished Textile Floor Covering Materials and ASTM D2859,
Standard Test Method for Ignition Characteristics of Finished Textile Floor
Covering Materials. All carpet sold and manufactured in the United States
must pass the pill test.

Because all carpet in the United States must pass the pill test and because
nearly all manufacturers of resilient and hard-surface materials provide
products that meet a Class I or II classification, specifying finish flooring
is usually not a problem when detailing platforms, stairs, and ramps.

Fire Resistance of Structural Flooring Components

In addition to finishes, the IBC regulates the types of materials that can
be used to construct raised platforms, stairs, and ramps. These are classified
generally as combustible or noncombustible. Combustible materials include wood,
while noncombustible materials include steel framing, concrete, and masonry.

For the purposes of fire and life safety, buildings are classified into
one of five categories, Type I, II, III, IV, or V. The classification is based
on the fire resistance of certain building components such as the structural
frame, bearing walls, floor construction, and roof construction. Type I construction
is the most fire resistive, and Type V is the least fire resistive. E.g.,
the structural frame of a Type I building must have a 3-hour rating, while
the frame in a Type III building must only have a 1-hour rating. In combination
with occupancy groups, building type limits the area and height of buildings.
Homes and small, one to three-story buildings are typical of Type V construction.

In Type I and Type II construction, any sub floor framing must be noncombustible
or the space between the fire-resistant floor of the building and the platform,
stair, or ramp must be solidly filled with noncombustible materials or fire-blocked
in accordance the IBC. Refer to the IBC for more information on construction
types and detailed requirements.

Some jurisdictions may allow the use of fire-retardant-treated wood to build
low platforms or stairs in Types I and II buildings. In all cases, the interior
designer should verify the type of construction and the requirements of the
local authority that has jurisdiction before detailing level changes and stairs and ramps.

There are special requirements for wood finish flooring in Type I and Type
II buildings.

Wood flooring may be attached directly to embedded or fire-blocked wood sleepers
or directly cemented to the top of the fire-resistant structural floor. Wood
flooring can also be attached to wood framing if it meets the requirements
described in the preceding paragraph. For Types III, IV, and V buildings,
wood framing may be used for any type of floor.

Refer to Section 2 for more information on fire tests for finish materials and construction
assemblies.

Two common safety problems with ground surfaces are slipping and tripping.
All surfaces should have slip resistance appropriate for the use. E.g., the
floor of a public lobby where snow and water are tracked in should be more
slip resistant than a private office. As discussed in Section 2, slip resistance
is commonly measured by the coefficient of friction (COF) and is a number
ranging from 0 to 1. A COF of 0.5 is considered a minimum value for floors.
For accessible routes a COF of 0.6 is recommended for level interior surfaces
and 0.8 for ramps. Refer to Section 2 for more information.

Tripping on level surfaces generally occurs because of a slight change in
level between two different materials or between the same materials installed,
so the edges are not flash.

When two materials abut, the designer should detail the joint so that the
two surfaces are as flash as possible. ADA requirements for accessibility limit
any change in level with a vertical surface to 1/4 in. (6.4 mm). A change in
level of up to 1/2 in. (13 mm) may be 1/4 in. (6.4 mm) vertical and 1/4 in.
(6.4 mm) beveled with a slope not steeper than 1:2 (13 mm); that is, 1/4 in.
(6.4 mm) high and 1/2 in. (13 mm) horizontal. Further, ADA requirements limit
the pile height of carpet to a maximum of 1/2 in. (13 mm) measured from the
top of the carpet to the backing. Ideally, there should be no vertical changes
in level from one material to another with all changes made with sloped or
beveled surfaces or transition materials. See ---- for details of some transitions.

Accessibility

In addition to the accessibility requirements for floor surfaces stated above,
the designer must also consider other accessibility issues when detailing ramps and stairs.

Ramps cannot slope more than 1 unit in height for every 12 units in length.
Thus, a ramp rising 14 in. (356 mm) must be at least 14 ft. (4267 mm) long
in horizontal projection.

However, whenever possible ramps should be designed with a slope less than
1:12, both to make it easier for people to use and also to allow for any
construction tolerances when the ramp is constructed.

Ramps must be at least 36 in. (915 mm) wide between handrails. Handrails must
be provided on both sides of the ramp when the rise is greater than 6 in. (150
mm). Level landings are required at the top and bottom of each ramp run.
The landing must be at least as wide as the width of the ramp for straight
runs and at least 60 in. (1525 mm) square when the ramp turns 90 degrees
or at least 60 in. (1525 mm) deep at a switchback. Other requirements for accessible
ramps are shown.

TT guard on open stairs min. 42" (1067) above nosing handrail returned
to wall, to newel post, or floor

-- Code Requirements

Building codes regulate the type, number, and width of egress stairways
as well as detailed requirements for treads, risers, and handrails. Most
of these are part of the architecture of a building. However, for the types
of stairs described in this section that consist of only a few risers and are
often detailed by interior designers, the code requirements for step design and handrails
still apply.

In most cases, the IBC requires handrails on both sides of stairs. The exceptions
for interior use include the following:

_ Aisle stairs in some situations

_ Stairways in dwelling units

_ Spiral stairways

_ Single risers in Group R-3 occupancies

_ Changes in room elevation of three or fewer risers within dwelling units and sleeping
units in Group R-2 and R-3 occupancies ( E.g., apartments, dormitories, and non-transient
hotels, and occupancies where the occupants are primarily permanent in nature
not otherwise classified as R-1, R-2, or R-4) However, even if handrails are
not required, they should be provided for safety and convenience.

The basic requirements for stairways and handrails are shown. The ends of
handrails must return to a wall, guard, or the walking surface or be continuous
to the handrail of an adjacent stair flight (or ramp run in the case of ramps).
Refer for more guidelines on stair design.

On open stairways, the IBC requires that a separate guard or low wall, in
addition to the handrail, be provided at 42 in. (1067 mm) above the height
of the nosing. The guard must be solid or designed so that there are no openings
that allow the passage of a sphere 4 in. (102 mm) in diameter. Refer to the
IBC for exceptions to this requirement.

The issue of where handrails are required for monumental stairs (those not
required for egress) can be confusing and sometimes contradictory. Of course,
handrails should always be located on each side of any stairway. When the width
of the stairway exceeds 60 in. (1524 mm), the IBC requires intermediate handrails
such that all portions of the stairway width required for egress capacity are
within 30 in. (762 mm) of a handrail. Thus, a wide stair that serves a small
occupant load for egress purposes may not need intermediate handrails.

E.g., assume that a wide monumental stair serves a raised platform on the
first floor of a retail store and has handrails on both sides. Each handrail
would be within 30 in. (762 mm) of egress width for a total of 60 in. (1524
mm). The IBC requires a minimum egress width for stairways of 0.3 in. (7.63
mm) per occupant served or, minimum width (inches) = occupant load × 0.3in.

Knowing that 60 in. is available the maximum occupant load that can be served
by these two handrails is, 60 in. = occupant load × 0.3in./occupant max. occupant
load = 60 in. 0.3in./occ. max. occupant load = 200 occupants If the platform
serves fewer than 200 occupants an intermediate handrail would not be required.
For a mercantile occupancy on the first floor, the IBC states a maximum floor
allowance per occupant of 30 sq. ft. In terms of a formula, occupant load =
floor-area 30 sq. ft./occ.

If the maximum occupant load for the handrails is 200 then, 200 occupants
= floor area 30 sq. ft./occ.

max. floor area = 200 × 30 max. floor area = 6000 sq. ft. (557 m^2).

Thus, the platform could be up to 6000 sq. ft. in area before intermediate
handrails would be required. However, the IBC also requires that monumental
stairs have handrails located along the most direct path of egress travel.
The issue then would be whether the sides of the stairway are along the most
direct path. This can be subject to interpretation. When the issue is questionable,
the designer should consult with the authority having jurisdiction for the
required location of intermediate handrails.

Handrails should be designed so that people can both grip them with maximum
effect and hold them by friction when pulling up or descending. A circular
shape with a diameter of 1-1/2 in. (38 mm) is generally the best, but other
shapes are allowed. See ---- for the allowable limits on handrail profiles
according to the IBC. The Type II handrail shown in (b) is allowed in private
homes and in selective residential situations in commercial applications.

Flooring design and detailing must be coordinated with flooring tolerances,
light reflectance and acoustic requirements, durability needs, and desired
circulation patterns. In addition, the design of the ground plane should be
coordinated with the overhead plane and how the connections between the floor and the
partitions are made. Refer to Sections 7 and 10 for
design ideas on overhead planes and how to make the floor-to-wall transition.

Tolerance Coordination

When carpet is used, the flatness tolerance of the sub floor is typically
not a concern. However, when hard-surfaced finish flooring is specified, the
sub floor on which it’s placed must be within certain tolerances for a successful
installation.

Some industry-standard tolerances for sub flooring are given. ---- lists some
requirements for the installation of finish flooring. In many cases, existing
sub flooring may exceed the requirements for a successful installation and the
interior designer will need to develop details or specifications to have the
sub flooring brought into compliance with finish flooring requirements. If
this includes using a leveling compound, the finish surface may be raised higher
than adjacent flooring. Grinding or patching existing sub floors will increase
costs. In new construction, the interior designer may coordinate with the architect
to create recessed areas for thick flooring material before the floor is constructed
to minimize this problem.

Light Reflectance and Acoustic Coordination

For lighting design, the r eflectance of the ground plane is generally the
least important surface, coming after the ceiling and the walls. This allows
the interior designer to specify nearly any color and texture for the floor
finish without adversely affecting light quality.

The floor's sound absorption can significantly affect the overall acoustic
quality of the space and should be selected with care. A hard-surface floor,
such as wood or resilient tile, will both r eflect sound and increase the
sound transmission to the floor below, both of which may be undesirable. E.g.,
the sound absorption average (SAA) (similar to the older NRC or noise reduction
coefficient) of 1/2-in. pile carpet on padding is about 0.50, while the SAA
of wood flooring is about 0.10. This means that carpet will absorb five times
the sound of the wood flooring in certain frequency ranges. Likewise, footfalls
on wood flooring can be easily transmitted to the floor below. If this is unacceptable,
other detailing options (such as sound-deadening board) must be used to minimize
the sound transmission, increasing cost and detailing complexity. Using carpet
would be a simpler approach.

METHODS

Detailing flooring material on concrete or wood substrates is usually straightforward.
The main detailing concerns for flooring other than carpet are accommodating
the total thickness of the finish material, making transitions from one material
to another, and allowing for tolerances and movement of the sub floor.
If terrazzo or thick-set tile or stone is used the ability of the floor to
carry the additional weight must be verified with a structural engineer.

Flooring

WOOD

For most commercial and residential applications either wood strip flooring
or thin parquet or laminated flooring is used. Other types of wood flooring,
such as plank, block, and resilient floor systems are not discussed in this
section.

Wood strip flooring is installed over a suitable nailing base by blind nailing
through the tongue of each strip of tongue-and-groove strip. ---- shows the
typical methods of detailing wood strip flooring over both wood and concrete
floors. For wood structures, the sub floor should plywood, particleboard, or
other suitable underlayment with a minimum thickness of 1/2 in. (13 mm). A
layer of 15 lb. asphalt felt may be laid to prevent squeaking and act as
a vapor barrier.

For concrete structures, either of the two methods may be used. Placing the
floor on wood sleepers gives a more resilient floor and provides
an air space that allows excess moisture to escape. However, it requires more
space and can be problematic when installing it next to a thinner floor.
The method, using a 3/4 in. (19 mm) thick plywood or particleboard base, requires
less total height but can still pose problems when abutted to much thinner
flooring such as resilient tile. In all cases it’s important to provide a minimum
3/4 in. (19 mm) expansion space at the perimeter of the room to allow for expansion and contraction
of the flooring.

Parquet and laminated flooring can be glued or loose laid over wood or concrete
sub floors. However, when such flooring is placed on a concrete sub floor,
especially a slab on grade, it’s critical that moisture not be present and the
slab be level to within 1/8 in. in 10 ft. (3 mm in 3 m).

Ceramic tile or quarry tile must be laid over a suitable substrate using one
of several formulations of mortar, or with adhesive. The joints are filled
with grout. Refer to Ceramic Tile: The Installation G uide by the Tile Council
of North America for a complete description of all the tile-setting methods.
The two basic methods of detailing are the thin-set method and the full-mortar-bed
method. Both of these are shown.

With the thin-set method tile is laid on a suitable substrate, commonly a
glass mesh mortar unit specifically manufactured for tile installation. This
is a cementitious panel nailed to the sub floor. The tile is then laid on a
thin coating of dry-set or latex-portland cement mortar.

The sub floor must be rigid to prevent cracking.

When excessive d eflection is expected (more than about 1/360 of the span)
or on precast and post-tensioned concrete floors, a full-mortar-bed detail
should be used. With this method, the tile and reinforced mortar bed are
separated from the structural floor with an antifracture membrane to allow
the two floor components to move independently. In addition to providing for
movement, this system allows minor variations in the sub floor level to be
corrected with the mortar. This is the preferred method (along with a waterproo
fing membrane) for tile floors in commercial showers or where continuous wetting
will be present. Because of the overall thickness required, this is one finish
flooring detail that should be placed on a sub floor depressed about 1-1/2
in. (38 mm), if possible.

With both the thin-set and full mortar bed methods of tile installation,
it’s important to provide for movement joints to prevent or control cracking.
Movement joints (sometimes called expansion joints) are required for large
expanses of tile and where the tile abuts re straining surfaces, such as
at columns, walls, and pipes. They are also required where backing materials
change and where dissimilar floors occur. They are not required in small
rooms or corridors less than 12 ft. (3660 mm) wide. ---- illustrates one type
of tile movement joint, and ---- gives the recommended joint widths and spacing.

Like ceramic tile, stone flooring can be installed with either the thin-set
method or the full-mortar-bed method. The full-mortar-bed method, while much
heavier, is used when the sub floor is uneven, where excessive d eflection
or movement is expected, or when the stone varies in thickness, as with slate
or sandstone. For most installations, current cutting and fabrication technology
make it possible to use thin tiles of natural stone rather than the traditional
3/4 in. (19mm) thick stone on a full mortar bed. However, for thin-set applications,
the floor must be level as given and not subject to d eflection or movement
more than about 1/720 of the span.

--- shows three methods of placing stone flooring on wood and concrete floors.

With the thin-set method, a uniform thickness of stone is set on the sub floor
with a special thin-set mortar or with an adhesive. The total thickness is
about 1/2 in. (13 mm) depending on the thickness of the stone tile. The full-mortar
bed method requires a layer of mortar from 3/4 in. to 1-1/4 in. (19 mm to 32
mm).

Stone floors can be set with the joints tightly butted together or with spaces
between joints. If there is a gap in the joint, it must be filled with grout
or a portland cement/sand mixture that can be color-coordinated with the stone.
Several types of grout are available that are resistant to chemicals, fungi, and mildew.
Latex grout is available and provides some flexibility when slight movement
in the floor is expected.

TERRAZZO

Terrazzo is a composite material that consists of marble, quartz, granite,
or other suitable stone chips in a matrix that is cementitious, modified cementitious,
or resinous. It’s typically poured in place but can also be precast. Terrazzo
is generally not detailed and specified by interior designers as a finish
material. Because of the additional weight and thickness required, it’s usually
part of the architecture of the building. It’s also messy to install and requires
time for pouring, curing, and grinding to complete the process. However,
terrazzo can be precast to avoid much of the on-site work required of standard
installations. Terrazzo does provide a very durable floor and the colors and styles
of the mixture can be varied between areas enclosed by the divider strips.
It’s also possible to design very ornate patterns using curved divider strips and different
color stone matrices.

There are various types of terrazzo installation methods, including the sand
cushion, bonded, monolithic, and thin-set methods. The sand cushion and bonded
methods are very heavy and require total installation thicknesses up to 2-1/2
in. (64 mm) thick. These are usually designed as part of the original architecture
of a building.

Monolithic terrazzo installations are applied directly to a concrete sub floor,
as shown. Terrazzo bases can be poured at the same time and provide a cove
base. This type of terrazzo installation is about 1/2 in. (13 mm) thick and weighs
about 7 lb. per ft^2 (3.4 kg/m2). The sub floor must be structurally capable
of supporting the extra weight without excessive d eflection. Divider strips
must be placed to provide areas of approximately 200 ft^2 to 300 ft^2 (19 m^2
to 28 m^2 ) in rectangular areas. The area of each area should not be more
than 50% longer than the width. Joint location should be coordinated with building
joints.

Thin-set terrazzo is similar to monolithic but only requires from 1/4 in to
3/8 in. (6 mm to 10 mm) thickness and weighs about 3 lb. per ft^2 (1.5 kg/m^2
). Thin-set terrazzo must use epoxy, polyester, or poly-acrylate matrices with
special types of divider strips.

Whenever one flooring material abuts another on the same level, there must
be some type of transition to prevent damage to the edges and to hold them
secure. This is true whether they are the same type of material or different
materials. As discussed there are three basic ways of making floor transitions:
by simply abutting the two materials, by placing a protective edge between
them, and by using a third material as a transition strip.

Abutting two materials without an intermediate material usually only works
when the two materials are the same type and are relatively hard. E.g., two
different types of stone flooring can be successfully abutted with a simple
grout joint as long as the finish surfaces are flash. Stone can be placed next
to ceramic tile with the same conditions. Conversely, the seam of two different
types and pile heights of carpet is susceptible to damage unless a transition
strip is placed over it.

Some type of protective edge is usually required when two materials abut.
This can be as simple as a metal angle or a manufactured transition strip designed
for specific types of flooring. (a) shows the application of a protective
edge angle. Refer to ---- for common sizes of stainless steel and brass shapes
that can be used to protect the edge of wood or stone flooring.

There are many types of manufactured wood, plastic, and metal transition
strips made for various materials and material thicknesses. --- shows some
common transition strips.

Refer to ---- for a listing of some of the manufacturers of transition strips.
Most resilient and wood flooring manufacturers supply their own line of transition
strips.

The designer can also detail custom transition strips and make them a design
feature between two flooring materials. These types of strips can be beveled
to accommodate the thicknesses of the flooring and made any convenient width.
See (b) and (c) for two different types of floor transition details using
a separate transition strip. The details show a beveled stone strip but hardwood
transition strips can also be used.

Handrails, Guards, and Stairways

As discussed in a previous section of this section, handrails are required
on both sides of all stairways used for egress and on monumental stairs if
they are used for egress. They should also be provided wherever needed for
safety. --- shows the basic requirements for handrail design. In addition,
the handrail design on an open stair as well as guards cannot allow the passage
of a 4 in. (102 mm) sphere. Guards are only required if the change in elevation
exceeds 30 in. (762 mm), but they should be used in all situations for safety.

When a change in level occurs the transition can be made in a number of ways
as discussed. The interior designer can detail custom railings and guards
from wood, metal, or some combination of materials. However, in most cases,
standard manufactured railing systems are used. These are available in a variety
of styles and materials and are custom modified by the supplier to fit
the exact requirements of the project. ---- lists some of the many manufacturers
of railing systems while ---- lists manufacturers of cable rail systems.

Guards can be designed with wood or metal top rails and with in fills of
glass, pickets, horizontal rails, mesh, perforated metal, or solid panels.
All-glass railings may be used with a top rail or without a rail for an open
appearance while providing for safety. See --- for one type of glass guard
detail. This detail can also be used for stairways with the addition of a handrail.

Stairs must be provided for raised platforms more than 7 in. (178 mm) high.
For most interior design work in spaces with low ceilings platform height is
limited, requiring only two or three steps. These are easily constructed of
wood or metal framing. Refer to Section 3 for guidelines on stair design.